This invention relates to apparatus for controlling or timing the operation of a controlled component in response to a given reference variable such as the angular displacement of a rotatable shaft, and deals more particularly with such an apparatus wherein the reference variable is converted by a transducer into a corresponding reference signal, used by the remainder of the apparatus, the magnitude of which uniquely identifies a corresponding magnitude of the reference variable.
The apparatus of this invention is intended for use with an active component or load having ON and OFF states and shiftable between such OFF and ON states by a control signal having corresponding OFF and ON values. In a common example, the controlled component is part of a machine, such as an automatic assembly machine, the operation of the component is to be synchronized with the rotation of a given shaft of the machine, and the motive power for the component is provided by an electric solenoid or the like which is sequentially energized and de-energized by the control signal as such signal switches between ON and OFF values. In this example, the reference variable is the angular displacement of the shaft from a given reference position.
A well known type of programmer for turning an associated component ON and OFF at preselected points in the rotation of a shaft is one using a cam fixed to the shaft and a number of switches mounted around the periphery of the cam and shifted between operated and un-operated conditions, as the cam rotates, by the surface of the cam itself or by switch operating pins or the like on the cam. The apparatus of this invention, in this application, is similar in broad function to such an arrangement, but instead of a mechanical cam employs a transducer for producing an output signal the magnitude of which identifies the shaft displacement or position. Other signals of the same character define the points in the shaft movement program at which switching of the control signal between its OFF and ON values is to occur, and a control signal generating circuit including comparators and a digital logic circuit produces a digital, ON and OFF valued, control signal from the shaft position reference signal and the set-point signals. Among other things, this means that only the transducer needs to be mechanically connected with the shaft and to be located on or in the machine. The output signal of the transducer may be conveyed by an appropriate communication line to a control station remote from the rotatable shaft and at which the other parts of the programmer are located. Also, the transducer output signal may be transmitted to both a terminal near the machine and another terminal at a remote control station, and the other parts of the programmer may be built as a portable module connectible to either the near terminal, as may be desirable when setting up the machine, or to the remote terminal, as may be desirable during normal running of the machine.
In other applications of the apparatus of the invention, the reference variable may be one, such as the linear displacement of a linearly movable machine element or a liquid level, which oscillates back and forth within a given range of values. In such applications, the apparatus of this invention can be used to serve the same function as more conventionally served in the past by a set of limit switches defining certain limit values of the reference variable.
Regardless of application, however, an important aspect of the invention is that the involved apparatus has two alternately available switching modes. Assuming that the reference variable is varied from a minimum to a maximum value, in one switching mode the control signal is initially ON so that its first transition is from ON to OFF and its second transition is from OFF to ON. In the alternate switching mode the control signal is initially OFF so that its first transition is from OFF to ON and its second transition is from ON to OFF. Furthermore, the selection of the switching modes is made automatically in response to the settings of the set-point devices without any other changes to the circuitry being required. In particular, one set-point device is dedicated to defining the ON set point at which the control signal goes ON (switches from OFF to ON) and the second set-point device is dedicated to defining the OFF set point at which the control signal goes OFF (switches from ON to OFF), and regardless of which set point is higher or lower than the other, the control signal will go ON at the ON set point and OFF at the OFF set point.
In the description which follows, the invention is shown by way of example to use a rotary resistance potentiometer as the reference variable to reference signal transducer, such potentiometer producing as the reference signal an output voltage having a magnitude analogous to the magnitude of an angular shaft displacement, the reference variable. However, it should be understood that the transducer may take various different forms and that its output need not necessarily be an electrical voltage signal. For example, where the reference variable is an angular shaft displacement, the transducer, instead of being a rotary resistance potentiometer may, among other things, be a rotary induction potentiometer, a selsyn resolver or an analog to digital shaft encoder. That is, the input to the transducer may be any of a large number of different kinds of reference variables and the output of the transducer may likewise by any one of a large number of different quantities such as pressure, force, displacement, frequency, shaft angle, electric current, electric voltage, etc. having a given characteristic the magnitude of which varies in accordance with variations in the magnitude of the reference variable so that each value of the reference signal represents a unique value of the reference variable. It should especially be understood that the reference signal need not necessarily be an analog signal, but may if desired be a digital signal representing a number the value or magnitude of which changes in accordance with changes in the magnitude of the reference variable.
In the description and claims which follow, and in the accompanying drawings, the two values which the control signal and other two valued digital signals may take are usually referred to as the ON and OFF values. When Boolean notation is used, the ON value is taken as the true or 1 value and the OFF value is taken as the false or 0 value.